Synthesis And Sodium Storage Performance Investigation Of Insert-type Transition Metal Compounds Anode Materials For Sodium-ion Batteries

Large-scale energy storage system(L-EES)is an effective tool to improve the rational and efficient utilization of electric power resources.Sodium-ion batteries(SIBs)show the advantages of high abundance,wide distribution,and low-cost for the resources,is an excellent choice for L-EES.This thesis started from satisfying the application of L-EES,aimed at stable performance,high-safety and rich resources insert-type anode materials for SIBs,and expanded from optimizaing existing materials to developing new materials.We optimized the NASICON type material NaTi₂(PO₄)₃(NTP)by using morphological design and potential regulation stratgegies firstly,and further developed a low-cost raw materials and easy-prepared novel Mn-based layered anode material Na₂Mn₃O₇.Besides,based on the unique structure of Na₂Mn₃O₇,a vacancy induction strategy for non-metal element doping of layered materials was porposed to improve the structural stability and electrochemical properties of the layered material.The specific contents are as follows:1.An open yolk-shell NaTi₂(PO₄)₃(ys-NTP)anode material was designed and synthesized by a facile,one-step,and template-free gel-hydrothermal method with solid-phase Ti source and based on the Ostwald ripening theory.The as-synthesized ys-NTP showed a uniform cubic morphology with the size about 1?m,which consists of a core about 700 nm and an open shell with a thickness about 50 nm.Benefited form the high Na⁺transfer efficiency that improved by the open yolk-shell structure and the high crystallinity that obtained during the ripening process,ys-NTP showed excellent electrochemical porperties.In addition,the sodium-ion full-cell assembled with Ni[Fe(CN)₆]PBA as cathode and ys-NTP as anode also exhibited decent battery performance,which possess the application potentials for L-EES.2.Aiming at the problem that NaTi₂(PO₄)₃ has a low reduction potential and easily overlaps with the decomposition potential of the electrolyte as the anode material for aqueous sodium-ion batteries,a potential regulation strategy was proposed and achieved the suppressing towards hydrogen evolution in the charging process at anode.By a redox couple substitution method,Na_1.5Ti_1.5Fe_0.5(PO₄)₃(NTFP)anode material was prepared,and exhibited a-0.721 V vs.Ag/Ag Cl operating potential under the synergistic effect of Fe³⁺/Fe²⁺and Ti⁴⁺/Ti³⁺redox couple,which deftly avoided the potential overlap with the reductive decomposition.The aqueous sodium-ion full-cell that matched with the Na_0.66Mn_0.66Ti_0.34O₂ cathode showed a nearly 100%charge-discharge coulombic efficiency and a 105 m Ah·g^-1 discharge specifica capacity with stable cycle over 300 times at 2 C,which is a highly stable and safe battery system that suitable for L-EES.3.A novel Mn-based layered insert-type anode material Na₂Mn₃O₇ was synthesized by a simple solid-state method using Mn which richer in resources and cheaper in price as the active element.The Na₂Mn₃O₇ exhibited a high discharge specifica capacity of 157.9m Ah·g^-1 that corresponding to the Mn⁴⁺/Mn³⁺redox reaction.The crystal structure of Na₂Mn₃O₇ belongs to the triclinic system P-1 space group,and has a unique honeycomb-like transition metal(TM)layer composed of Mn₆-ring that arranged by Mn O₆ octahedron.In addition,the novel dual-manganese based sodium-ion full-cell assembled with Na₂Mn₃O₇ as anode and Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂ as cathode showed decent battery performance.4.In order to further optimize the sodium storage performance of the novel material Na₂Mn₃O₇,based on its unique honeycomb TM layer structure,a vacancy induction strategy was proposed to achieve the non-metal element B doping in the TM layer of layered material Na₂Mn₃O₇.By introducing Na vacancies in the structure,the binding energy barrier of B bonding in the TM layer was reduced.B was successfully doped into the TM layer of the material and bonded at the Mn vacancy,stretched the adjacent Mn-O bonds and Na atoms,thereby caused a slight distortion of the crystal structure.The bonding of B in TM layer decreased the covalency of Mn-O bonds,the oxidation activity of the O atoms,and the diffusion barrier of Na⁺in the structure,thereby significantly improved the electrochemical properties of the material.The vacancy induction strategy provides a new perspective for the optimization of layered electrode materials.